A new potassium permanganate reagent with slow-release properties was designed and tested for possible application in in situ chemical oxidation. For this purpose, MnO(2)-coated KMnO(4) particles (MCP) were prepared by partial reduction of solid KMnO(4) using the acid-catalyzed reaction with n-propanol or the comproportionation of Mn(VII) and Mn(II) in n-propanol as reaction medium. Column tests showed that, for MCP with a residual KMnO(4) fraction of 70wt%, the duration of permanganate release under flow-through conditions was prolonged by a factor of 10 compared to untreated KMnO(4). While KMnO(4) is too soluble to be used in reactive barriers, MCP could be introduced into the aquifer by filling of trenches or boreholes; this would allow a prolonged passive dosing of permanganate into the flowing groundwater. In addition, experiments were conducted in order to determine the oxidation capability of native KMnO(4) particles and MCP in CH(2)Cl(2), a representative non-polar non-aqueous phase liquid (NAPL). It may be possible to utilize the significantly higher reactivity of MCP under these conditions for the design of slow-release permanganate particles for NAPL source treatment.